The Structure of the Earth and Plate Tectonics
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Transcript of The Structure of the Earth and Plate Tectonics
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The Structure of the Earth and Plate Tectonics
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Structure of the Earth
• The Earth is made up of 3 main layers:– Core– Mantle– Crust
Inner core
Outer core
Mantle
Crust
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The Crust• This is where we live!
• The Earth’s crust is made of:
Continental Crust
- thick (10-70km)- buoyant (less dense than oceanic crust) - older crust
Oceanic Crust
- thin (~7 km)- dense (sinks under continental crust)- Newer crust
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How do we know what the Earth is made of?
• Geophysical surveys: seismic, gravity, magnetics, – Acquisition of information: land, air, sea and satellite
– Geological surveys: fieldwork, boreholes, mines
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What is Plate Tectonics?
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• If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.
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Plate Tectonics• The Earth’s crust is divided into 12 major
plates which are moving in various directions.• This motion causes the plates to collide, pull
apart, or scrape against each other.• Each type of interaction causes a
characteristic set of Earth structures or “tectonic” features.
• The word “tectonic” refers to the deformation of the crust as a consequence of plate interaction.
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World Plates
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What are tectonic plates made of?
• Plates are made of rigid lithosphere.
The lithosphere is made up of the crust and the upper part of the mantle.
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What lies beneath the tectonic plates?
• Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.
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Plate Movement• “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells
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What happens at tectonic plate boundaries?
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• Divergent
• Convergent
• Transform
Three types of plate boundary
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• Spreading ridges– As plates move apart, new material erupts from
the mantle to fill the gap
Divergent Boundaries
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Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
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• Iceland has a divergent plate boundary running through its middle
Iceland: An example of continental rifting
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• There are three styles of convergent plate boundaries– Continent-continent boundaries– Continent-oceanic crust boundaries– Ocean-ocean boundaries
Convergent Boundaries
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• Forms mountains, e.g. European Alps, Himalayas
Continental-Continental Collision
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Himalayas
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• This is called SUBDUCTION. A deep ocean trench forms at the edge of the continent.
Continental-Oceanic Crust Collision
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• Oceanic lithosphere subducts, or goes underneath the continental lithosphere
• Oceanic lithosphere heats and dehydrates as it subsides
• The melt rises, forming volcanic mountains such as the Andes
Subduction
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• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
• The deepest parts of the ocean are found along trenches.
The Mariana Trench in the western Pacific Ocean is 11,033 meters (36,201 feet) deep. To put this in perspective, Mount Everest, the highest mountain in the world, is 8,848 meters (29,028 feet) tall.
Ocean-Ocean Plate Collision
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• Where plates slide past each other
Transform Boundaries
Above: View of the San Andreas transform fault
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Earth’s Crustal Plates
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…what’s the connection?
Volcanoes and Plate Tectonics…
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Volcanism is mostly focused at plate margins
Pacific Ring of Fire
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- Subduction - Rifting - Hotspots
Volcanoes are formed by:
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Pacific Ring of Fire
Hotspot volcanoes
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• Hot mantle plumes breaching the surface in the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain is an examples of hotspot volcanoes.
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The tectonic plate moves over a fixed hotspot, forming a chain of volcanoes.
The volcanoes get younger from one end of the chain to the other.
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…what’s the connection?
Earthquakes and Plate Tectonics…
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As with volcanoes, earthquakes are not randomly distributed over the globe
At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.
Figure showing the distribution of
earthquakes around the globe
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Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
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Plate Tectonics Summary• The Earth is made up of 3 main layers; the core, the
mantle and the crust)• On the surface of the Earth are tectonic plates that are
slowly moving around the globe• Plates are made of the crust and upper part of the mantle
(lithosphere)• There are 2 types of plates, oceanic and continental• There are 3 types of plate boundaries: convergent,
divergent and transform• Volcanoes and earthquakes are found at the edges of
tectonic plates